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    <title>DOM </title>
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    <p>
        <b>querySelectorAll() 获取的NodeList 不是实时更新的，只是一个快照</b>
        <b>qs 获取不到元素，或者解析错误，会抛出错误</b>
        <b>可用 node.matches() 判断是否能获取到元素</b>
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